Continuous measurement of viscosity

ABSTRACT

A viscometer is provided which operates on the principle of an oscillating or vibrating tongue or reed and includes means for bringing the surrounding liquid to be measured into laminar flow in the vicinity of the tongue.

United States Patent [1 1 Kleinschmidt 1 Dec. 11, 1973 CONTINUOUSMEASUREMENT OF VISCOSITY Inventor: Ernst Kleinschmidt, Schildgen,

Germany Herbol-Werke Herbig-Haarhaus e sti n sss l s t kayd. vNordrhein-Westfalen, Germany Filed: Oct. 8, 1971 Appl. No.: 187,698

[73] Assignee:

Foreign Application Priority Data [52] U.S. Cl. 73/59 1m. c Go g/1n I[58] Field oisirhg 73/54, 59, 32 A,

[56] References Cited UNITED STATES PATENTS 3,393,553 7/1968Kleinschmidt 73/54 Primary Examiner-Richard C. Queisser AssistantExaminer-Joseph W. Roskos Attorney-Johnston, Root, OKeeffe, Keil,Thompson & Shurtleff [57] ABSTRACT A viscometer is provided whichoperates on the principle of an oscillating or vibrating tongue or reedand includes means for bringing the surrounding liquid to be measuredinto laminar flow in the vicinity of the tongue.

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. body provided with openings on both sides and surrounding the endportion of the measuring probe.

In chemical processes rapid and continuous measurement of the viscosityof liquid and semiliquid media is often a great importance since itenables conclusions to be drawn as to the progress of the reaction.

A viscometer for reaction mixtures in stirred vessels operating on theprinciple of the vibrating tongue is already known from U.S. Pat.3,393,553 according to which the measuring probe is surrounded by a tubewhich is circular in cross-section, which extends beyond the measuringprobe on both sides and which is open on both sides, the said tube beingconstricted in the direction of flow of the reaction mixture enteringthe tube up to the tongue and thenceproceeding cylindrically to theoutlet, and its internal diameter at the location of the tongue beingsuch that laminar flow prevails at this point. Other features of theprior art apparatus are that the tube is turned up like a funnel at thepoint of entry of the reaction mixture and the probe is surrounded by aconical jacket having a convex front end which provides with the tubeenclosing it an annular space of practically constant size for thepassage of the reaction mixutre. The accurancy of measurementsachievable with the prior art measuring meansdepends largely on the flowwithin the stirred vessel which is determined by the design of thestirred vessel, the stirring speed, the presence of cooling or heatingcoils in the stirred vessel and on obstacles to flow in the vicinity ofthe measuring point such as dip tubes for thermometers, gas inlet pipesfor inert gas and the like.

The objects of the present invention is to provide means that do nothave the disadvantages of the prior art means and which achieve alaminar flow in the vicinity of the vibrating tongue irrespective of theflow of the liquid, so that high accuracy ofmeasurement is ensured andinfluences disturbing the measurement are substantially avoided.

This object is achieved in accordance with the invention by means forproducing a laminar flow of liquid along the vibrating tongue, saidmeans being arranged beyond the free end of the tongue.

The invention prevents the vibrations of the tongue being disturbed,e.g. by undesirable particles present in the liquid such as insolublematerial, gel or skin particles, overcondensed or underpolymerizedsubstances, and also vapors and the like.

In a special embodiment of the invention the measuring probe is locatedin a cylindrical tube open at both ends, a funnel-shaped widened tubeportion attached to a cylindrical portion of the tube containing thecoil being arranged around the tongue. In this way a suction force isexerted which acts on the immediate environment of the tongue and which(a) maintains the continuous flow of reaction mixutre past the tongueand (b) removes extraneous particles from the vicinity of the tongue.

According to another embodiment of the invention the end portion of themeasuring probe incorporating the tongue is located in a cylindricalcontainer which Y 2 narrows from the free end of the tongue and which isattached by the constricted portion to a hollow body open at both ends.

In a further embodiment of the invention the hollow body open at bothends has at least one constriction of its cross-section so that asuction effect is created in the interior of the container. It is thuspossible to arrange a straight measuring probe with the tongue in axialdirection in the stirred vessel although the flow in the stirred vesselis predominatly transverse to the axis of the stirred vessel.

According to yet another embodiment of the invention, the measuringprobe is located in a bypass of the stirred vessel which incorporatesmeans for producing the flow of the reaction mixture. Betteraccessibility and therefore a better control of the measuring probe isthus achieved.

Other features of the invention may be seen from the accompanyingdrawings and the following description of some embodiments.

The diagrammatic drawings show:

In FIG. 1 a stirred vessel, partly broken away, with a greatly enlargedmeasuring probe is a container;

In FIGS. 2 to 4 a straight measuring probe in a cylindrical container;

cooling coil 4 is shown. A thermometer 5 is provided in a dip tube on aside wall 6 of the vessel. A measuring probe 7 may be seen greatlyenlarged in stirred vessel 1. The lower end of the measuring probe 7projects into a cylindrical container 8 which beyond the end of a tonge9 of the measuring probe 7 has a funnel-shaped constrictuion and at thisconstriction 10 there is provided a tube 11, open at both ends, arrangedtransversely to the axis of the measuring probe and also constructed atthe point of attachment. The measuring probe passes thorugh the wall ofthe stirred vessel 1 at 12. An electrical lead extends outsides to ameasuring instrument 13 having a scale 14. One half of the tongue 9consists of a magnetostrictive metal alloy and is arranged in a coil 15,and the second half, consisting of stainless and acid-resistant steel,dips into the reaction mixture to be measured. The tongue 9 is vibratedfrom the measuring instrument 13 by means of ultrasonic waves, thevibration causing shear stresses in the boundary surfaces of thereaction mixture. The damping of the vibrations of the tongue thuseffected produces a change in the electrical data in the excitationcircuit which is visible on the scale 14 as a deflection of the pointer.Naturally the measured values may be recorded by means of recordingmeans (not shown).

FIG. 2 shows measuring probe 7 on an enlarged scale. Container 8 isshown in section so that the end portion of measuring probe 7 and tongue9 are visible. Above tongue 9, coil 15 is indicated which normally isenclosed by the measuring probe. Container 8 has beneath its cover 16,around is casing, openings 17 for the reaction mixture to enter asindicated by arrows l8 and 19. At the constricted portion 10 of thecontainer there is attached a narrow cylindrical tube 20 which opensinto a narrowed portion 21 of tube 11. The reaction mixture flowsthrough the constriction in tube 11 at a greater speed than through thenormal tube crosssection. According to Bernoullis principle a decreasedpressure is produced in container 8 so that the reaction mixture entersthrough openings 17 into the container whose cross-section is chosenhaving regard to the Reynolds number so that a laminar flow is producedin the interior, passes tongue 9 in laminar flow and then flows awaythrough portion 21 and tube 11. Flow through tube 11 is produced by thestirring movement of blade 3. This flow, however, only has importance asa means for producing the decreased pressure, whereas the flow incontainer 8 is kept laminar and constant, substantially independently ofthe flow in the stirred vessel. Undesirable particles and vapors aresucked out as quickly as possible from the environment of the tongue sothat the vibration of the tongue 9 is not hindered and accurate resultsare obtained. In FIGS. 3 and 4 the measuring probe is again located incontainers 8 as in FIG. 2 and corresponding parts therefore have thesame reference numbers. It is merely the decrease in pressure which isproduced by other means in the embodiments of FIGS. 3 and 4. In FIG. 3,the cylindrical tube 20 opens into a tube 22 of constant diameter.Upstream of the point where tube 20 passes into tube 22 a constrictionis provided by securing in tube 22 a tubular portion 23 having a smallerdiameter which is widened at one end. In FIG. 4 the cylindrical tube 20passes into a tube 24 widened in the direction of flow and having at oneend a nozzle 25 through which an inert gas, for example nitrogen, isforced, so that reduced pressure is produced in container 8. In FIG. theangled measuring probe 26 enters a tube 27 which narrows in thedirection of flow. Around the angled portion of the measuring probe 26 aguttiform flow guiding member 28 is provided and the coil (not shown) isenclosed by a cylindrical tube portion 29 to which is attached a funnelportion 30 around tongue 9. The constricted tube cross-section is formedbetween the tube 27 and the funnel portion 30. FIG. 6 shows a stirredvessel 1 according to FIG. 1. A measuring tube 33 is attached at thebottom 32; the tube 33 has an S- shaped bend and leads to a device 34known as a pulsometer. The pulsometer is connected with the upperportion of the stirred vessel 1 through a lifting pipe 35 and has athird tube attachment 36 for the supply of compressed gas. The measuringprobe is introduced between the vertical portion of the S-shaped bendand the pulsometer where it is easily accessible. The curvature of thetube and the diameter, especially in the vicinity of the measuring probe7, are similarly determined by the Reynolds number whose value of lessthan 2,400 is a prerequisite for a laminar flow. In the path of themeasuring tube 33 there are arranged a shutoff valve 37, a sieve 38, arelief valve 39, a resistance thermometer 40 and a nonreturn valve 41.Nonreturn valve 41 prevents backflow of the liquid in the measuring tube33 and prevents damage to measuring probe 7. A pump of known type may beused instead of the pulsometer 34. In this embodiment also theproduction of a laminar flow of the reaction mixture along the tongue 9is ensured by means of a pulsometer 34 located beyond the free end oftongue 9. The flow produced by stirring blade 3 is illustrated in thedrawing by arrows l. The tubes 11, 22, 23, 24 and 27 are formed withtheir surfaces closed.

The embodiments of the invention described above relate to themeasurement of viscosity in the production of synthetic resins andpolymers. The measuring apparatus may also be used successfully in theproduction of synthetic resins when an entrainer, for example xylene, isused for esterification and the elimination of water associatedtherewith.

Accurate results are achieved with less susceptibility to trouble in themeasuring apparatus when measuring means as shown in the drawings areused. It has been found that for example vapors are sucked off from thetubes or containers in which tongue 9 is located and there is continuousflow of liquid past tongue 9, which can be concluded from the fact thatthe viscosity rises continuously with the reaction time at constanttemperature.

I claim:

1. A device for the continuous measurement of the viscosity of a liquidreaction mixture, in particular a reaction mixture in a stirred vessel,which comprises a viscosimeter having a vibrating tongue and including atubular measuring probe supporting the tongue on one end, the tonguebeing positioned within a container between openings in the containerfor the entry and exit of one stream of the liquid reaction mixture, thecontainer having a portion extending beyond the free end of the tongue,and said portion being provided with a substantially constricted flowcross-section and communicating with a tubular section for a secondstream of the said reaction mixture to induce a laminar flow along thetongue at a Reynolds number of less than 2,400.

2. A device as claimed in claim 1, wherein said container is ofsubstantially cylindrical shape and has said constricted portiondownstream of the free end of the tongue, and said constricted portionbeing attached to a narrowed portion of said tubular section, the latterbeing provided with inlet and outlet openings for said second stream ofthe liquid reaction mixture.

3. A device as claimed in claim 1, said tubular section comprising anouter tube having its flow cross-section reduced by an inner tube withinsaid outer tube.

1. A device for the continuous measurement of the viscosity of a liquidreaction mixture, in particular a reaction mixture in a stirred vessel,which Comprises a viscosimeter having a vibrating tongue and including atubular measuring probe supporting the tongue on one end, the tonguebeing positioned within a container between openings in the containerfor the entry and exit of one stream of the liquid reaction mixture, thecontainer having a portion extending beyond the free end of the tongue,and said portion being provided with a substantially constricted flowcross-section and communicating with a tubular section for a secondstream of the said reaction mixture to induce a laminar flow along thetongue at a Reynolds number of less than 2,400.
 2. A device as claimedin claim 1, wherein said container is of substantially cylindrical shapeand has said constricted portion downstream of the free end of thetongue, and said constricted portion being attached to a narrowedportion of said tubular section, the latter being provided with inletand outlet openings for said second stream of the liquid reactionmixture.
 3. A device as claimed in claim 1, said tubular sectioncomprising an outer tube having its flow cross-section reduced by aninner tube within said outer tube.